A variety of solid-phase assay tests for detection or quantitation of solution analytes have been proposed. In a typical test of this type, a test solution is added to a solid-phase reagent which is coated with ligand molecules capable of binding specifically to the analyte, or with molecules effective to compete with the analyte for binding to reporter-labeled anti-ligand molecules. After incubation under binding conditions, the solid-phase reagent is washed to remove unbound sample material, and "developed" to allow detection of analyte or analyte-competing molecules bound to the reagent.
In one general assay format, the solid-phase reagent is a card or multi-well device having a number of surfaces which are coated, e.g., by chemical derivatization, with ligand molecules. In another general format, the solid-phase reagent is a bead or particle coated with ligand molecules. The bead is usually carried in a well, with the various solution addition and removal steps involved in an assay procedure being carried out by careful solution transfer to and from the well.
One advantage of ligand-coated particles, in an solid-phase immunoassay, is that the particles can De prepared more easily in bulk and with greater uniformity, in terms of ligand coating density, than ligand-coated wells or surfaces. Another advantage is that the surface concentration of detectable analyte-related reporter molecules on a particle is effectively higher than on a planar surface, both because of the curvature of the particle and, where the particle is optically transparent, because of the ability to detect reporter molecules on front and back sides of the particle.
It would be desirable to provide an assay device which utilizes ligand-coated particles or beads, to exploit the advantages discussed above, and which also permits easy manufacture, bead capture, and flexibility in designing a system for determination of a selected group of analytes.